Visualize running container counts on tree root and group nodes

[SATYAM-PRATIBHAN]

Description

This PR improves container visibility in the tree view when nodes are collapsed or grouped, which is especially helpful in environments with many containers.

Dynamic status summaries were added to the description field of the Containers root node and individual container group nodes (such as Docker Compose projects). This makes it possible to see container state at a glance without manually expanding nodes.

Key Changes

• Root Node: Displays (X running) next to the Containers label when one or more containers are active.
• Group Nodes: Displays (X/Y running) next to group names, showing the number of running containers versus the total number of containers in that group.
• Base Class Refactor: Updated LocalRootTreeItemBase and LocalGroupTreeItemBase to safely expose item data to subclasses, enabling these summaries while following existing architectural patterns.
• Unit Tests: Added a new test suite at src/test/tree/containers/ContainerTreeVisualization.test.ts to verify the description logic for both root and group nodes.

Related Issue

Fixes #485

Visuals

Before:

After:

Testing

• Manual verification: Verified in Extension Development Host that descriptions update correctly when containers start and stop.
• Type checking: npm run build:check passed successfully.

[SATYAM-PRATIBHAN]

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